Pipeline packers are designed for injection into the pipeline through a launching tube, either as a single tool or in pairs, for the purpose of isolating predetermined sections of pipe for repair or replacement or a valve or other equipment in the isolated zone. The packer is propelled to the designated location using the flow of product in the line with the packer being tracked from above the ground using known techniques. Upon reaching the desired location, fluid flow in the line is terminated and the packer is activated by a signal from the operator on the surface to form a seal against the inner pipeline wall. Once the packer is properly set, the section of pipeline downstream of the lock-up needing repair or replacement is isolated by means of a second packer or a block valve. Pressure in the isolated section of line is relieved and the product therein removed to create a proper working environment without having to drain or depressurize the adjacent sections of pipeline.
When the portion of pipeline to be repaired is completely drained, that portion can be physically removed for replacement. On completion of the repair, the operator will transmit another signal to release the packer which is then moved away by resuming the flow of pipeline product for removal from the pipeline through an adjacent launch tube or pig trap.
Packers are relatively well known in the prior art, and reference is made in this regard to U.S. Pat. Nos. 4,422,477, 4,854,384 and 5,293,904 as well as Canadian Patent 1,292,704 and Canadian laid-open patent Application No. 2,042,338. The latter reference is more specifically directed towards a pipeline pig which, as will be appreciated by those skilled in the art, is designed to fulfil a different purpose than a packer and functions quite differently.
Packers of the present sort generally comprise an expansible elastomeric seal to form a fluid-tight barrier against the inner pipeline wall. These seals alone are insufficient to lock the packer in position against the often extremely high fluid pressures exerted by the pipeline product. Hydraulic pressure is therefore used to drive a set of slips or brake shoes into gripping contact with the inner pipeline wall. The slips or brake shoes are typically wedge-activated so that the differential or delta pressure acting across the packer will actually increase the force exerted by the brake shoes on the pipeline wall to ensure an even stronger grip. It is vital that the packer be firmly locked in the pipeline. In the event of failure, the packer may be expelled at velocities more than sufficient to crush workers in the repair zone and to create the potential for an ecological disaster.
Although packer design has been improved substantially over the years, known tools still suffer major drawbacks. Most importantly, known tools can withstand product pressure from one side of the packer only and must therefore be properly oriented to form a seal against head pressure acting from the design direction. This limits versatility.
Existing tools moreover are designed to perform a single sealing operation and must then be withdrawn from the pipeline for valve replacement and/or power source recharge prior to reuse. For example, a commonly used power source is compressed nitrogen over hydraulic fluid stored in a separate accumulator. To set the tool, the hydraulic fluid is released to the head that sets the slips by means of valves opened using explosive charges. When the job is complete, another explosive valve is blown to exhaust the hydraulic fluid into the pipeline, thereby releasing the tool. The packer's power supply is now completely exhausted and the tool must be removed from the pipeline for recharge of the accumulator and replacement of the explosive valves. This is time consuming and expensive and highlights the need for a packer having true multiset capabilities.
Another drawback to existing packers is the inability to equalize pressure across the packer following completion of the pipeline repair and before release of the tool. Typically, prior to release of the packer, the repaired section of line is tapped for fluid reintroduction. The packer release valve is then blown using charges, the pipeline flow is resumed and the packers are removed at the next adjacent pig trap. The packers are then serviced and re-energized. It would be advantageous to provide a packer having a built-in bypass system actuatable to allow fluid flow through the packer itself for equalization of the pressure across the tool without having to perforate the repaired section.